Diabetes Insipidus

Question 1

2 stimulus of secretion of ADH

Answer 1

1. Volume contraction causes increased ECF osmolarity, which stimulates the osmoreceptors in the hypothalamus
   Stimulation of the osmoreceptors stimulates ADH secretion
2. Hypotension stimulates volume receptors, which stimulates ADH secretion

Question 2

Actions of ADH

Answer 2

ADH stimulats reabsorption of water int eh distal tubules and collecting ducts
This results in increased water in ECF and decreased ECF osmolarity
Increased ECF osmolarity also stimulates the thirst center and increases water uptake
Increased water uptake increases water in ECF and decreases ECF osmolarity

Question 3

Use of ADH

Answer 3

Natural ADH (pitressin) is administered IM or IV over 1 hour in lactated ringer’s or 5% dextrose for diagnosis of Diabetes Insipidus

Question 4

Types of Diabetes Insipidus

Answer 4

Central DI = caused by ADH deficiency
Nephrogenic DI = caused by impaired responsiveness of the kidney to ADH
DI is associated with polyuria and polydipsia

Question 5

3 Treatment Options for Central DI

Answer 5

1. Desmopressin, DDAVP - drug of choice for CDI in dogs and cats
2. Thiazide Diuretics - minimal effect on CDI
3. Chlorpropamide - not very effective treatment of CDI in dogs and cats

Question 6

Desmopressin, DDAVP

Answer 6

A synthetic ADH analog
More potent and has a longer duration of action than natural ADH
Minimal vasoconstrictor action (more selective on V2 than V1)
Given parenterally (SC, IM, IV) and the nasal drops are instilled into the conjunctival sac

Question 7

Chlorpropamide

Answer 7

An oral hypoglycemic sulfonylurea drug

Requires the presence of some endogenous ADH to act

Question 8

Treatment for Nephrogenic DI

Answer 8

Thiazide diuretics are the drug of choice for NDI

Question 9

Dietary restriction for both CDI and NDI

Answer 9

Restricted NaCl intake is useful in both CDI and NDI